Process for making durable rutile titanium dioxide pigment by vapor phase deposition of surface treatments

Abstract

The present invention relates to a process for making durable titanium dioxide pigment by vapor phase deposition of surface treatments on the titanium dioxide particle surface by reacting titanium tetrachloride vapor, an oxygen containing gas and aluminum chloride in a plug flow reactor to form a product stream containing titanium dioxide particles; and introducing silicon tetrachloride into the reactor at a point down stream of the point where the titanium tetrachloride and oxygen were contacted and where at least 97% of the titanium tetrachloride has been converted to titanium dioxide or where the reaction temperature is no greater than about 1200° C., and preferably not more than about 1100° C.

1. A method to determine a point of introduction of silicon tetrachioride into a plug flow reactor for the oxidation of a mixture of titanium tetrachloride and aluminum trichloride in a gas containing at least a stoichiometric amount of oxygen to produce titanium dioxide rutile particle having a thin, uniform and complete layer of surface oxides comprising a mixture of amorphous aluminum oxide and silicon dioxide, the steps of the method comprising;
 (a) reacting titanium tetrachloride vapor and aluminum chloride and at least a stoichiometric amount of oxygen in a plug flow reactor to form a product stream containing titanium dioxide particles;  
 (b) determining the temperature in the reactor where not more than 3% of the titanium tetrachloride remains unreacted using 
       K   =         [       2   ⁢     (       100   ⁢   %     -     u   TiCl4       )       +     ϕ   ×   100   ⁢   %       ]     2         u   TiCl4     ⁡     (     β   +     u   TiCl4       )             
     and     
       T   <       20733       ln   ⁢           ⁢   K     +   6.391       -   273.15         
 where,  
 
       U TiCl4 =unreacted TiCl4(%)  
       β=O2(%) in excess of the stiochiometric amount  
       φ=feed Cl2 mole ratio (mol/mol TiCl4), and  
       T=temperature (C);  
       and
 c) introducing the silicon tetrachioride into the reactor where the temperature is equal to or less than the temperature determined in step (b).  
 
     
     
       2. The method of  claim 1  wherein the temperature determined in step (b) is no greater than about 1200° C. 
     
     
       3. A process for making durable rutile titanium dioxide pigment by vapor phase deposition of a surface treatment on the titanium dioxide pigment particle surface, the process comprising:
 (a) reading titanium tetrachioride vapor and aluminum chloride and at least a stoichiometric amount of oxygen in a plug flow reactor to form a product stream containing titanium dioxide particles;  
 (b) determining the temperature in the reactor where not more than 3% of the titanium tetrachloride remains unreacted using 
       K   =         [       2   ⁢     (       100   ⁢   %     -     u   TiCl4       )       +     ϕ   ×   100   ⁢   %       ]     2         u   TiCl4     ⁡     (     β   +     u   TiCl4       )             
     and     
       T   <       20733       ln   ⁢           ⁢   K     +   6.391       -   273.15         
 where,  
 
       U TiCl4 =unreacted TiCl4(%)  
       β=O2(%) in excess of the stiochiometric amount  
       φ=feed Cl2 mole ratio (mol/mol TiCl4), and  
       T=temperature (C);  
       and
 (c) introducing silicon tetrachloride into the reactor where the temperature is equal to or less than the temperature determined in step (b).  
 
     
     
       4. The process of  claim 3  wherein the temperature determined in step (b) is no greater than about 1200° C. 
     
     
       5. The process of  claim 3  wherein the silicon tetrachloride is introduced in an amount sufficient to provide a silica content of a surface treated titanium dioxide pigment of about at least 1.2% by weight and aluminum trichloride is present in an amount sufficient to provide an aluminum oxide content of a surface treated pigment of at least about 1% by weight. 
     
     
       6. The process of  claim 3  wherein steam or oxygen is introduced at a point downstream of the point of introduction of silicon tetrachloride or wherein steam or oxygen are introduced along with the silicon tetrachioride.